1. Field of the Invention
The present invention relates to an apparatus for attaining variable control of valve timing in an internal-combustion engine.
2. Description of the Prior Art
Variable control is used to obtain valve timings which can be adapted to various engine operating conditions, such as low-speed and high-speed operation. Many types of such apparatuses have heretofore been proposed. The most typical type of such apparatus includes a mechanism by which the angular relationship between a crankshaft and a camshaft connected thereto is changed. The mechanism conventionally includes differential gears or planetary gears.
A certain degree of backlash inevitably occurs due to the fact that a torque is generated in one direction when the valves open, this direction being opposite to the direction in which a torque is generated when the valves close. This generated backlash causes operational noise to increase and transmission efficiency to decrease.
In order to eliminate the drawbacks encountered in the prior art, in a co-pending patent application, the inventors of the present invention previously proposed a variable valve-timing apparatus wherein a pair of sleeves is connected to a camshaft and a crankshaft, respectively, of an internal-combustion engine. Adjacent slits angled relative to each other are formed in the sleeves. Abutment rollers are arranged in the slits in such a manner that the abutment rollers linearly move along the axis of the camshaft. Due to such a straight movement of the abutment rollers arranged in the corresponding slits, a relative angular displacement is generated between the sleeves so that valve timing may be varied.